What is Fault Tree analysis in Health and Safety? Is Fault tree analysis a Qualitative or Quantitative Risk assessment?

What is Fault Tree analysis in Health and Safety? Is Fault tree analysis a Qualitative or Quantitative Risk assessment?

Risk assessment is of two type .i.e. Quantitative and Qualitative. Quantitative risk assessment means prioritizing the risk through its quantification. Like in 5 X 5 risk assessment matrix, risk prioritized on the basis of Severity and Probability. We multiply both severity and probability and higher the number higher the risk. This ranking or numbering gives us an idea about dealing the high number risk prior to low number risk. This is called as Quantitative risk assessment and Fault tree analysis is one of the quantitative risk assessment techniques as well as qualitative too.

Qualitative risk assessment means no quantity and hazard, risk identified from the activity. After identification of hazard and risk we apply control. There is no priority, no ranking. This is called as qualitative risk assessment. Example of qualitative risk assessment is Job safety analysis (JSA).

Fault Tree analysis

Facts about Fault tree analysis are as below:

1-      Regularly used technique in High hazard industries like Chemical, aerospace, nuclear power station.

2-      Top down based

3-      Deductive failure analysis

4-      Mathematical technique used for large and complex processes.

5-      Based on Boolean algebra (Use of 0 and 1)

Steps to perform an event tree analysis:

Define the system: Define what needs to be involved or where to draw the boundaries.

Identify the accident scenarios: Perform a system assessment to find hazards or accident scenarios within the system design.

Identify the basic events: Basic events are at bottom of the graphical representation, here basic events mentioned in the picture are failure of sprinkler system in case of fire, fail to call Fire department etc..

Identify Top events: Graphically represent top event interacting to cause total loss. Like here we mentioned in the picture Fire as a Top event.

Obtain event failure probabilities: If the failure probability can be obtained by use of fault tree analysis.

Document the FTA: Document the entire process on the Fault tree diagrams and update for new information as needed.

Advantages:

Fault tree analysis can be used to:

1-      Understand the logic leading to the top event / undesired state.

2-      Show compliance with the (input) system safety / reliability requirements.

3-      Prioritize the contributors leading to the top event - Creating the Critical Equipment/Parts/Events lists for different importance measures.

4-      Monitor and control the safety performance of the complex system (e.g., is a particular aircraft safe to fly when fuel valve x malfunctions? For how long is it allowed to fly with the valve malfunction?).

5-      Minimize and optimize resources.

6-      Assist in designing a system. The FTA can be used as a design tool that helps to create (output / lower level) requirements.

7-      Function as a diagnostic tool to identify and correct causes of the top event. It can help with the creation of diagnostic manuals / processes.

Example:

In the below given picture we have considered Top event as “Fire”

Qualitative Fault tree diagram suggest below things:

1-      Consequence 1- Fire happens and in case Sprinkler work and fire department called then “No” damage happened.

2-      Consequence 2- Fire happens and Sprinkler worked but didn’t called fire department or didn’t called on time the Partial damage may happen.

3-      Consequence 3- Fire happens and sprinkler not worked but fire department called then also Partial damage may happen.

4-      Consequence 4- Fire happens and both function not worked. Sprinkler not worked and Fire department not called then Total system destroyed damage happen.

Reference: https://en.wikipedia.org/wiki/Event_tree_analysis